[build] enable concurrent compilation

[ahorek]

this significantly reduce build time

[mgreter]

IMO this is not really portable, what about mingw on windows?

[ahorek]

yes, I was worried about the same thing. mingw on windows doesn't really support concurrent compilation, but it won't fail, the option is just ignored.

[mgreter]

Actually mingw does support concurrent compilation, but nproc is not installed and will therefore fail.

[ahorek]

-j option is supported, but it has no effect on windows, it's still single threaded (gcc version 8.2.1 mingw)

I've changed that to -j 0 (autodetect), so now the code doesn't rely on nproc

[mgreter]

I use gmake quite regularly and used dmake before (it uses -PXX insteal of jXX).
It definitely does compile in parallel, not sure which make flavor you mean that ignores it.
Otherwise I'm fine if 0 means autodetect, but could you please add a more descriptive
title/description to the commit? Always useful to have meaningful git logs! Thanks!

[ahorek]

done, I've added a benchmark aswell. On my AMD FX-8300 8C it's 4,6x faster.

[xzyfer]

Thanks

[richardwhiuk]

Surely this is the wrong fix - shouldn't the caller control the fanout by passing make -j 0 if they want this behaviour.

Currently this causes unbounded fan out, which is deeply wrong, and it ignores a caller passed in setting - e.g. make --jobs 1 will be overriden by this change - which is happening when the Rust build attempts to control fanout to the number of CPUs - see compass-rs/sass-rs#53

Compilation on my box now regularly fails with:

STDERR:virtual memory exhausted: Cannot allocate memory
make: *** [src/ast_sel_cmp.o] Error 1
make: *** Waiting for unfinished jobs....
virtual memory exhausted: Cannot allocate memory
virtual memory exhausted: Cannot allocate memory
virtual memory exhausted: Cannot allocate memory
virtual memory exhausted: Cannot allocate memory
virtual memory exhausted: Cannot allocate memory
virtual memory exhausted: Cannot allocate memory
virtual memory exhausted: Cannot allocate memory
make: *** [src/cssize.o] Error 1
make: *** [src/fn_numbers.o] Error 1
make: *** [src/fn_selectors.o] Error 1
make: *** [src/extend.o] Error 1
make: *** [src/inspect.o] Error 1
make: *** [src/remove_placeholders.o] Error 1
make: *** [src/fn_utils.o] Error 1

[xzyfer]

Sounds reasonable. Open to reverting this change.

[ahorek]

ok, sorry, I tested again and you're right. -j 0 is indeed unlimited. The original nprocs limit was removed because it's hard to get the value safely on all platforms. I've reverted the change in #2977

btw optflags https://github.com/sass/libsass/pull/2977/files#diff-b67911656ef5d18c4ae36cb6741b7965L19 also can't be overridden.